1. Field of the Invention
The present invention relates to a variable magnification copying machine and, more particularly, to a variable magnification copying machine capable of widening the magnification range without unduly extending the optical path length.
2. Description of the Prior Art
Copying machines for varying the magnification of an image of an original (to be referred to hereinafter as a variable magnification copying machine) have been popular in recent years. Two variable magnification schemes are available for conventional variable magnification copying machines. One system is a U variable system wherein the focal length of a lens system is fixed, and the optical path length U extending from an original surface to an image forming plane is changed to vary the magnification, as described in Unexamined Patent Publication (Kokai) No. 58-40518. The other system is a U fixed system wherein the optical path length U extending from the original surface to the image forming plane is fixed, and the focal length of the lens system is changed to vary the magnification, as described in Unexamined Patent Publication (Kokai) No. 59-2026.
In the conventional U variable system, the optical path length must be changed until a desired magnification is obtained. If the variable range of magnifications, that is, the variable magnification range is widened, the optical system inevitably becomes bulky. In the conventional U fixed system, the focal length of the lens system must be changed until a desired magnification is obtained.
If the variable range of magnifications, that is, the variable magnification range is widened, the number of lenses constituting the lens system must be increased. In addition, the diameter of the lenses is also increased. As a result, the optical system inevitably becomes bulky. As an end result, in either system, when the variable magnification range is widened, the optical systems of the conventional U fixed and U variable systems are inevitably characterized by a large size. As a result, the copying machine becomes undesirably bulky.